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The field inventory did reveal a potentially dangerous situation involving the use of wire rope clips and thimblesas a terminal end attachment. As discussed in the cable saddle section, a wire rope must have a proper bendingradius. Proper diameter wire rope thimbles should be used with wire rope that is manufactured for flexibility.This usually means a larger number of wire in a strand, such as a 6 x 49 construction. Structural bridge ropethat is 7 x 7 or 6 x 7 should not be used with thimbles and wire rope without recognition that this combinationresults in a 50 percent reduction in the bridge rope strength. Structural bridge rope has a large bending radiusrequirement. It is manufactured to be used with spelter or swaged sockets.

Suspender Design and Installation

The primary purpose of the suspenders is to transfer the walkway load to the catenary cables. The stiffeningtrusses distribute a point live load to several suspenders. This reduces the vertical oscillations of the walkwayunder non-uniform loading. The suspender design and installation had to meet several criteria; they had to be:

• Structurally sound.

• Vandal resistant.

• Minimum number of parts or connections.

• Have a vertical adjustment capacity.

• Practical to install under adverse conditions.

• Cost-effective with no adverse impact on public safety.

The first five would be easy to accomplish if it was not for the sixth criteria. The final suspender design isdetailed on Plan Sheet 8 and Figure 16.

The suspender assembly utilized for the Pochuck Quagmire Bridge is more sophisticated, but at the same timesimpler than suspender assemblies for similar bridges. Working top to bottom, as detailed on Plan Sheet 8,Figure 16, and photographs 59-62, the individual components are as follows:

• CM Big Orange Piggyback wedge socket clip attachment to the catenary cable.

• Flemish eye loop with a 1/2-inch extra heavy duty wire rope thimble and flemish sleeve.

• 1/2-inch 6 x 19 galvanized EIP IWRC wire rope.

• Muncy 1-inch thread stud, electro zinc galvanized, swaged to the 1/2-inch wire rope.

• 1 1/16-inch bore hole through 6-inch by 6-inch cross-stringer.

• 3-inch by 3-inch by 3/16-inch galvanized square washer.

• 1-inch bore galvanized square washer.

• Standard 1-inch square nut.

• 1-inch lock nut (not shown in construction photos).

A distinguishing feature is the vertical adjustment capability by utilizing the threaded stud.

Practical elements and concerns about vandalism became the determining factors in the suspender design ratherthan pure structural criteria. The number and 5-foot spacing of the suspenders was determined by the designof the cross-stringers. The design of the cross-stringers was in turn influenced by the size of the borehole

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Figure 16. Cross-stringer suspender detail.

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Photo 58. Suspender connectionon the PQB. Photo courtesy of Mr.Tibor Latincsics.

required to pass the threaded rod. A 4-inch by 6-inch cross-stringer would have been sufficient from a loadingperspective, but the project engineer was concerned about the long-term impact of the 1 1/8-inch bore hole.Would the 4-inch by 6-inch cross-stringer crack at the bore hole when the bridge shifted in the wind? Thisconcern resulted in the 6-inch by 6-inch cross-stringers being specified for the suspenders. Slightly over-sizingthe suspender bore hole had two benefits. The first ensured that the threaded rod would easily pass througheven if the cross-stringer swelled if it became wet prior to assembly. This was a prudent precaution because thePochuck Quagmire Bridge was eventually assembled in torrential rains. The second benefit was to allow a littleplay in the system so the cross-stringer would not spilt as the bridge shifted in the wind. Vandalism concernsdetermined the 1/2-inch 6 x 19 wire rope being specified. The 1/2-inch wire rope has a nominal breakingstrength of 13 tons, which is far in excess of the 650 pound design load on each suspender. However, using asmaller diameter seemed to invite vandals to “snip” the critical connector. This is a prudent precaution for thePochuck Quagmire Bridge location as it is in a relatively remote, unsupervised location yet accessible to a widevariety of users. Local youths were drinking beer and “recreating” at the site before the bridge was finished.

The upper end of the wire rope terminates in a flemish loop, which is shown in photo 58. The flemish loop iscreated by the galvanized heavy duty thimble and the crimped flemish sleeve. The flemish sleeve is theweak link of the suspender assembly in that it has a rated capacity of 2.4 tons. This is typical of the fact thatconnections are the “weak link” in a structural system. The flemish loop was used in lieu of three wire ropeclips typically used for this connection. Shown in photo 59 is the wire rope clip suspender connection of theAppalachian Trail Tye River Bridge.

The flemish loop offers the followingadvantages:

• Vandal resistant.

• Strong.

• Cost-effective.

• Arrives prefabricated - fewersmall parts to accidentally dropinto the river.

• Less long-term maintenance.

• Better looking - professional endproduct.

However, the flemish loop does not havethe in-the-field adjustment capability ofsimple wire rope clips. This adjustmentcapability is provided by the threadedrods at the lower end of the PochuckQuagmire Bridge suspender assembly.

This shall be discussed later. One should be aware that using a flemish loop requires accurate calculation ofsuspender lengths.

Photos 58 and 60 show the CM Big Orange Piggyback clip that provides the interconnection between thesuspender and catenary cable. Also provided are three photographs of alternate connections used on otherbridges inspected in the author’s inventory. A comparison of these four structurally acceptable alternativesprovides an interesting contrast of practical elements and costs. All costs are presented in 1996 dollars.The drop forged CM Big Orange Piggyback clip provides a direct connection from the flemish loop thimble to

Photo 59. Suspender connec-tion on the Appalachian TrailTye River Bridge. Photo courtesyof Mr. Tibor Latincsics.

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Photo 63. WMNF LincolnWoods Trail Bridge clampto rod suspender. Photocourtesy of Mr. TiborLatincsics.

the catenary cable. The number of parts required are minimized. The piggybacks cost $22.50 each. Photo 61shows the method used on the Tye River Bridge. Although the bridge was originally built in 1972, the walkwayand suspender assemblies were replaced in 1992 because several suspenders had corroded to the point of beingunsafe. The connection consists of a 1-inch Crosby drop forged wire rope clip and a 7/8-inch screw pin chainshackle. The cost for this connection hardware is $35.98. The cost is so high because individual chain shack-les are a specialty item. One might ask, “Why not connect the flemish loop with just the wire rope clip andeliminate the shackle?” This would result in the two wire ropes rubbing against one another every time thebridge is loaded or the wind blows. Such a wear point could lead to long-term problems.

The third alternative, as shown in photo 62, was used on the Jackson River Bridgein Virginia. It is a 1-inch wire rope clip and chain shackle in concert with a halfopen swage socket. This is a good connection, which addresses the vandalism andmaintenance problems of numerous wire rope clips. The cost is $59.08.

The fourth alternative, which is a bridge clamp, is shown in photo 63. Thisparticular one is on the Lincoln Woods Trail Bridge off the Kangamangus highwayin White Mountain National Forest. They are also used on other suspensionbridges built by the USDA Forest Service in the White Mountains. The bridgeclamps cost $108 each and are a specialty item having a long delivery time. Ignor-ing the cost-benefit ratio, it is the best wire rope connector. The cost of the fouralternatives, if used for the 42 Pochuck Quagmire Bridge suspenders, is as follows:

Pochuck Quagmire Bridge piggybacks (42) ($22.50) = $945Tye River clip and shackle (42) ($35.93) = $1,511Jackson River swage socket (42) ($59.08) = $2,481White Mountain bridge clamp (42) ($108.00) = $4,536

Photo 60. PQB CM Big OrangePiggyback Clip and flemish loop.Photo courtesy of Mr. Tibor Latincsics.

Photo 61. Appalachian Trail TyeRiver Bridge Crosby Clip, chainshackle, and wire rope. Photocourtesy of Mr. Tibor Latincsics.

Photo 62. Jackson River BridgeCrosby Clip, chain shackle, andswage socket. Photo courtesy ofMr. Tibor Latincsics.

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The $4,536 cost and long delivery time required for the bridge clamps was not within the project scope. Sucha cost would have been 13 percent of the total project budget. A long delivery time would have doomed theproject, which depended on accelerated construction during a narrow construction “window” in the PochuckQuagmire. The Pochuck Quagmire Bridge piggybacks meet the six design criteria listed at the beginning of thissection.

The next major elementof the suspenderassembly is the connec-tion to the 6-inch by 6-inch cross-stringer.This was performed byswaging a 30-inch long,1-inch diameterthreaded stud to the1/2-inch wire rope.The threaded stud isshown in photos 64 and65, Figure 16 on page59, and detailed on Plan

Sheet 8. The swaged threaded stud provides another vandal proof simple connection. A swage connection is avery structurally sound connection developing 95 to 100 percent of the wire rope strength. The threaded studwas simply threaded through a 1 1/8-inch vertical bore hole in the cross-stringer.

This provides two major benefits.

• The threaded stud provides a vertical adjustment capability to fine tune the bridge camber. Thiscapability should not be used as a reason not to accurately calculate the various suspender lengths.

• As shown in photo 64 and Figure 16, by beveling the underside of the 6-inch by 6-inch cross-stringerto the slope of the bridge camber,the bridge walkway is automati-cally set to the desired slope. Inthis case that was 3.5 percent.The suspender hangs vertical(plumb) and the 3-inch by 3-inchbearing washer is perpendicular tothe suspender and flush to thebeveled underside of the cross-stringer.

These two design componentssaved a significant amount of timein the bridge construction. Photo68 on page 63 shows an alterna-tive to the threaded rod used onthe Tye River Bridge – a turn-buckle connected to an eyebolt.This alternative is not as desirableas the threaded rod for the

Photo 65. Threaded rod through cross-stringer. Flat washer on top and bottom.Photo courtesy of Mr. Tibor Latincsics.

Photo 64. Underside 3.5 percent bevel cuton the 6-inch by 6-inch cross-stringer setthe walkway slope. Photo courtesy of Mr.Tibor Latincsics.

Photo 66. Suspender assembly.Photo courtesy of Mr. Tibor Latincsics.

Photo 67. Suspender assembly —top view. Photo courtesy of Mr. TiborLatincsics.

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following reasons:

• Turnbuckles are easily vandalized and are high maintenance.

• More wirerope clip connec-tions and connec-tions in generalare needed.

The WhiteMountain ForestService Bridgesuse a U-bolt tomake the stringerconnection, asshown in photo69. This providesa limited verticaladjustment

capability. The White Mountain Bridges have a distinct design feature inthat the suspenders are a steel rod with a welded loop at either end. Theloop connects to the bridge clamp at the top and the stringer U-bolt at thebottom. While the White Mountain Bridges appear to be very successful,this method may have the following limitations:

• Manufacturing the steel rod to the correct length is difficult and time consuming.

• There is little or no long-term adjustment capability to account for wood shrinkage or cable stretch.

• The rigid steel rods transfer walkway oscillations to the catenary cables more readily than the wire ropesuspenders.

The combination of longer threaded U-bolts, bevel cut on the stringer underside, and a flemish sleeve connec-tion would give a designer the ability to specify adjustability, walkway slope, and cradle all at the same time.

A Practical Lesson – “The Hard Way”

The installation of the piggyback clips provided a hard-learned lesson, which is applicable to other projects.The catenary cables and suspenders were fabricated by Mr. Dick Doran, an internationally known wire ropeexpert, of Doran Sling. As was the case with almost everyone who came in contact with the project, Mr.Doran became interested in the project on both a professional and personal level. He provided a wealth ofpractical information. The project specifications called for the catenary wire rope to be cut in the shop andthe spelter sockets attached. The suspenders would be fabricated to the varying correct lengths and mountedon the primary catenary at calculated locations. The entire prefabricated assembly would then be reeled onan oversized spool and transported to the bridge site for installation. Due to their interest in the project, aswell as keeping the accelerated construction schedule going, GPU Energy volunteers offered to pick up thecable early and mount the suspenders in the field. This would be done while the prefab of the bridge walk-way was proceeding at Wawayanda State Park. The suspenders were not mounted in the shop. Out in thefield (in 6 inches of mud and pouring rain), it was discovered the seat of the 1-inch piggyback clips wouldnot snug up to the 1-inch wire rope. This would have been a minor problem in the Doran shop, but out in the

Photo 69. U-bolt connection. Dry River Bridge, WMNF.Photo courtesy of Mr. Tibor Latincsics.

Photo 68. Suspender - stringerconnection on Appalachian Trail TyeRiver Bridge, GW & JNF. Photocourtesy of Mr. Tibor Latincsics.